木本植物对CO_2浓度和温度升高的相互作用的响应

CO2 浓度和温度是影响木本植物生长和发育的两个关键因子 ,二者在全球变化中的相互作用对木本植物生长和发育具有显著的影响。大多数研究表明 :CO2 浓度增加和温度升高的相互作用可能影响木本植物的生长发育 ,促进光合作用 ;呼吸作用对CO2 浓度增加和温度升高的相互作用存在长期和短期响应差异 ;二者的相互作用促进生物量增加和生产力的增长。木本植物对CO2 浓度和温度升高的相互作用的响应程度因植物种类而异。     

不同密度红桦幼苗苗冠结构与竞争对CO2浓度升高的响应

研究了两个种植密度下,红桦（Betula albosinensis）苗冠结构特征对CO2浓度的响应,在此基础上探讨了CO2浓度升高对植物竞争压力的影响。结果表明,冠幅、冠高、苗冠表面积和苗冠体积均受CO2浓度升高的影响而增加,但是受密度增加的影响而降低。CO2浓度升高对苗冠的促进效应在低密度条件下大于高密度处理,高密度条件下苗冠基本特征部分地受到CO2浓度升高的促进作用;升高种植密度的效应则在高CO2浓度条件下大于现行CO2浓度处理。高CO2浓度和高密度条件下,LDcpa（单位苗冠投影面积叶片数）、LDcv（单位苗冠体积叶片数）和苗冠底部枝条的枝角均低于相应的现行CO2浓度处理和低密度处理,这主要是由于冠幅和冠高的快速生长所造成的。升高CO2浓度对枝条长度的影响与枝条在主茎上所处位置有关。总之,升高CO2浓度有利于降低增加种植密度对苗冠所带来的负效应,而增加种植密度降低了升高CO2浓度的正效应。LDcpa和LDcv的降低表明,红桦在升高CO2浓度和种植密度的条件下,会作出积极的响应,从而缓解由于生长的增加所带来的竞争压力的增加。     

亚高山林线优势种形态结构和竞争力对CO2浓度和温度升高的响应

利用封顶式生长室模拟未来变化的气候条件,研究了亚高山林线优势物种岷江冷杉(Abies faxoniana)和4种草本植物形态与竞争指标对CO2浓度和温度升高的响应.结果表明:处理2个生长季后,高CO2浓度条件下,岷江冷杉冠体积增加42％,比叶面积、比冠体积和比根长分别增加17％、65％和19％;温度升高使岷江冷杉冠形更纵向生长,冠体积增加22％,根冠比和比根长均比对照增加17％;二者同时升高使岷江冷杉冠体积增加79％,比叶面积、比冠体积和比根长分别增加17％、197％和18％.CO2浓度升高处理下糙野青茅(Deyeuxia scabrescen)的株高、基茎和每株叶片数增加,但比叶面积降低;甘肃苔草(Carexkansuensis)、东方草莓(Fragaria orientali)和紫花碎米荠(Cardamine tangutorum)的各项指标变化与青茅相反.温度升高下青茅、苔草、草莓株高、基茎和根冠比下降.二者同时升高条件下4种草本植物的基茎和每株叶片数增加,但比叶面积和根冠比降低.这表明,在CO2浓度和温度升高处理下,岷江冷杉形成有利于生长的冠层结构且单位质量的竞争力增加,而4种草本植物的形态结构和竞争力均受到不同程度的负面影响.     

干旱区胡杨光合作用对高温和CO2浓度的响应

采用LI-6400便携式光合作用测定仪实测的塔里木河下游胡杨(Populus euphratica oliv)光合作用参数,探讨了不同地下水埋深下的胡杨光合作用对CO2浓度增加和温度升高的响应.结果表明:(1)CO2浓度升高减小了胡杨气孔导度,促进了光合速率、胞间CO2浓度和水分利用效率的增加,但不同地下水埋深下,胡杨光合作用参数对CO2浓度升高的响应不同,干旱环境(地下水埋深较深)下的响应程度大于水分适宜(地下水埋深浅)环境下的响应;(2) 高温引起胡杨气孔发生不完全关闭,导致了光合作用的光抑制发生,从而降低了胡杨光合速率,但降低程度受水分条件的影响,地下水埋深较深环境下的影响程度大于地下水埋深浅的;(3)地下水埋深是控制干旱区胡杨光合作用对CO2浓度和温度升高的根本因素,6m是胡杨生长正常的临界地下水埋深,地下水埋深>6m,胡杨即遭到水分胁迫,地下水埋深>7m,胡杨即受到了较严重的水分胁迫.     

CO２浓度和温度升高对11种植物叶片解剖特征的影响

以生长在严格控制的温度梯度,以及温度和CO2浓度梯度2个温室里的8种美国中西部弃耕地常见草本植物和3种美国东部落叶阔叶林优势木本植物为材料,通过比较叶片栅栏组织厚度、海绵组织厚度、和叶片总厚度的变化,探讨CO2浓度和温度升高对不同功能型植物叶解剖特征的影响。结果表明：当温度升高时,C4植物的叶片厚度增加,而C3植物叶片厚度的变化无明显规律;当CO2浓度升高时,9种C3植物中有7种植物的叶片总厚度增加,而C4植物叶片厚度减少。植物叶片解剖特征沿CO2浓度和温度梯度呈现线性和曲线变化趋势;不同物种的同一组织厚度和同一物种的不同组织厚度,对温度和CO2都升高或仅仅温度升高的反应都存在很大的差异。在未来全球变化情况下,植物叶片对CO2和温度升高的反应存在明显的种类差异。由于植物的结构和功能是相关联的,这种解剖结构的改变将可能引起植物功能上对CO2和温度升高反应的差异。     

烟草在PVY~N病毒与烟蚜作用下对高CO_2浓度的响应

以CO2浓度为主处理因子,研究了加倍CO2浓度和对照大气CO2浓度条件下,烟蚜、马铃薯Y病毒N株(PVYN)以及二者共同作用下烟草各指标的响应。结果表明,在当前CO2浓度条件下,PVYN、烟蚜及两者联合作用对烟草生物量影响不显著;而在未来高CO2浓度条件下,PVYN、烟蚜及两者联合作用对烟草生物量影响很大。CO2浓度升高后,PVYN和蚜虫二者联合作用显著降低烟草产量,危害加重,高CO2的"肥料"作用被极大地削弱。在有烟蚜、PVYN以及两者共同作用时烟草的化学物质及主要的次生代谢物烟碱的含量对CO2浓度升高的响应也发生一定的变化,表现在:高CO2浓度条件下,蚜虫、蚜虫与PVYN共同作用显著增加了烟草的含氮量;显著减少了烟叶含糖量;PVYN及其与蚜虫共同作用显著升高叶片可溶性蛋白含量;当高CO2浓度下,各处理的烟草烟碱含量均显著下降,而且PVYN感染的烟叶烟碱含量无论在哪一种CO2浓度条件下,都比无毒无虫的对照烟叶烟碱含量升高。结果显示,烟蚜和马铃薯Y病毒N株(PVYN)对烟草的产量、营养物质及防御物质都有影响;CO2浓度升高对烟草的生长有促进作用,增加了烟草的产量,但蚜虫的危害和PVYN感染使烟草产量下降,在高CO2浓度条件下,烟蚜和PVYN共同作用相对于目前CO2浓度对烟草产量的危害加重。     

棉花对大气CO2浓度升高的响应及其对棉蚜种群发生的作用

通过模拟试验研究了棉花对大气 CO2 浓度升高 (70 5 .0 μl/ L 和 10 32 .3μl/ L vs.387.4 μl/ L)的响应及其对棉蚜 (Aphisgossypii Glover)种群发生的作用机制。结果表明 :(1) CO2 浓度升高可以促进棉花的生长 ,显著提高棉花的株高和生物产量 ;(2 )CO2 浓度增加对棉花的光合作用十分有利 ,单株叶面积显著增加 ,同时 ,叶绿素含量也显著增加 ;(3)高的 CO2 浓度可明显影响棉花组织的营养成分和次生代谢物质的含量 ,游离脂肪酸和游离氨基酸显著增加 ,可溶性蛋白含量显著降低 ,此外 ,大气 CO2增加下棉花组织内棉酚和单宁含量也显著增加了 ;(4 )棉蚜的发育历期与棉花组织的游离脂肪酸、游离氨基酸、可溶性蛋白、和棉酚的含量呈显著负相关 ;而棉蚜的繁殖力与组织含水量呈显著负相关 ,与游离脂肪酸、游离氨基酸和棉酚的含量呈显著正相关。大气 CO2 浓度升高主要是通过影响棉花的营养组成和次生代谢物质含量 ,而间接作用于棉蚜 ;未来 ,随着大气 CO2 浓度增加 ,棉花组织营养物质的变化对棉蚜种群的发生和危害有加重的趋势     

自由大气CO2浓度升高对夏大豆生长与产量的影响

IPCC报告指出到本世纪中期全球大气CO2浓度将比目前的浓度增加50%.CO2浓度升高将影响大豆的生长及产量.有关大气CO2浓度对大豆影响的研究大多在温室或开顶式气室中进行的,利用FACE (Free Air CO2 Enrichment)系统对大豆生长发育受CO2浓度升高影响的试验首次在中国进行,FACE圈中心的CO2浓度维持在(550±60)μmol·mol-1,对照浓度(389±40)μmol·mol-1.这是继美国SoyFACE之后世界第二个利用FACE系统对大豆生长发育进行的研究,研究表明:大气CO2浓度升高提高了两个大豆品种全生育期的叶、茎、荚重及地上部分总重,收获后地上部分总干重平均提高52.30%;大豆叶面积对CO2浓度升高的响应存在品种差异,中黄35促进叶面积增加而中黄13抑制叶面积的增加.CO2浓度升高使鼓粒期大豆比叶重增加,中黄35比叶重增加23.08%到达显著水平.CO2浓度升高使大豆节数、分枝数、茎粗提高,特别是茎粗收获期中黄35增加7 18%,中黄13增加26.33%,均到达显著或极显著水平;大气CO2浓度升高使两个品种产量平均增加30.93%,产量的增加主要是由于CO2浓度升高提高了大豆单株荚数和百粒重.大气CO2浓度升高对大豆各器官占地上部分重量的比例影响不明显,对大豆收获指数的影响未达显著水平.大气CO2浓度升高对大豆的影响品种差异明显.结论与美国SoyFACE的研究结果基本一致,如FACE系统下大豆生物量、产量都较对照增高,但变化幅度较SoyFACE的结果高.     

大气CO_2增加对不同生长光强下龙须菜光合生理特性的影响

为了探讨未来大气CO2升高对不同生长光强下大型海藻的影响,选取经济红藻龙须菜为实验材料,研究了其生长速率、光合作用、呼吸作用、叶绿素荧光参数以及光合色素对CO2和光强的响应。实验设置两个CO2浓度,正常空气水平CO2浓度(390μL/L)和高CO2浓度(1000μL/L);两个光强梯度,高光(300μmol m-2s-1)和低光(100μmol m-2s-1)。结果表明,CO2和光强对龙须菜的生长和光合作用有明显的交互作用。大气CO2升高并没有显著影响龙须菜的生长速率,但在不同CO2处理下,龙须菜对光强的响应不同。在空气水平下,光强的变化对其生长速率影响不显著。而在高CO2作用下,高光处理下的藻体有更高的生长速率。CO2显著促进高光生长下龙须菜的呼吸作用速率,但是在低光下作用不明显。而对于光合作用速率来说,低光培养下的藻体CO2表现为负面效应,但对高光下生长的藻体作用不明显。CO2增加没有改变龙须菜生长状态下的电子传递速率,但在高光下,CO2表现为一定的抑制作用。CO2显著降低了龙须菜天线色素藻红蛋白和叶绿素a的含量。这些CO2与光强的结合效应表明,大气CO2的升高对龙须菜光合生理特性的影响随着光强的变化而呈现不同的效应,在未来评估CO2的增加对大型海藻的影响时,要充分考虑其他环境因子的耦合效应。     

大气二氧化碳浓度增加对木本植物BVOCs释放的影响

植物挥发性有机化合物(biogenic volatile organic compounds,BVOCs)在近地表臭氧和二次有机气溶胶生成中有重要作用,而大气CO2浓度上升对植物BVOCs释放有显著影响。利用Meta-analysis方法对已发表的数据进行整合分析发现:(1)总体而言,大气CO2浓度增加会导致不同木本植物(常绿与落叶)BVOCs释放降低;(2)就不同木本植物BVOCs释放而言,大气CO2浓度增加主要导致落叶植物BVOCs释放速率降低,而常绿植物则以增加为主;(3)就植物释放BVOCs种类而言,大气CO2浓度增加显著降低异戊二烯的释放速率,对单萜烯释放速率则无显著影响。结果可为阐明陆地生态系统BVOCs释放对全球CO2浓度增加的响应提供依据。     

Acclimation to temperature of the response of photosynthesis to increased carbon dioxide concentration in Taraxacum officinale

The relative stimulation of photosynthesis by elevated carbon dioxide in C₃ species normally increases strongly with increasing temperature. This results from the kinetic characteristics of Rubisco, and has potentially important implications for responses of vegetation to increasing atmospheric carbon dioxide. It is often assumed that because Rubisco characteristics are conservative, all C₃ species have the same temperature dependence of the response of photosynthesis to elevated carbon dioxide. However, in this field study of Taraxacum officinale, there were no significant differences in the relative stimulation of photosynthesis by elevated carbon dioxide among days with temperatures ranging from 15 to 34 °C. Nevertheless, short-term measurements indicated a strong temperature dependence of the stimulation. This suggested that acclimation to temperature caused the lack of variation in the seasonal data. Experiments in controlled environments indicated that complete acclimation of the relative stimulation of photosynthesis by elevated carbon dioxide occurred for growth temperatures of 10 – 25 °C. The apparent specificity of Rubisco for carbon dioxide relative to oxygen at 15 °C, as assayed in vivo by measurements of the carbon dioxide concentration at which carboxylation equalled oxygenation, also varied with growth temperature. Changes in the apparent specificity of Rubisco accounted for the acclimation of the temperature dependence of the relative stimulation of photosynthesis by elevated carbon dioxide. It is premature to conclude that low temperatures will necessarily reduce the relative stimulation of photosynthesis caused by rising atmospheric carbon dioxide. This revised version was published online in June 2006 with corrections to the Cover Date.     

The influence of increasing growth temperature and CO2 concentration on the ratio of respiration to photosynthesis in soybean seedlings

Using controlled environmental growth chambers, whole plants of soybean, cv. ‘Clark’, were examined during early development (7–20 days after sowing) at both ambient (≈ 350 μL L^–1) and elevated (≈ 700 μL L^–1) carbon dioxide and a range of air temperatures (20, 25, 30, and 35 °C) to determine if future climatic change (temperature or CO₂ concentration) could alter the ratio of carbon lost by dark respiration to that gained via photosynthesis. Although whole-plant respiration increased with short-term increases in the measurement temperature, respiration acclimated to increasing growth temperature. Respiration, on a dry weight basis, was either unchanged or lower for the elevated CO₂ grown plants, relative to ambient CO₂ concentration, over the range of growth temperatures. Levels of both starch and sucrose increased with elevated CO₂ concentration, but no interaction between CO₂ and growth temperature was observed. Relative growth rate increased with elevated CO₂ concentration up to a growth temperature of 35 °C. The ratio of respiration to photosynthesis rate over a 24-h period during early development was not altered over the growth temperatures (20–35 °C) and was consistently less at the elevated relative to the ambient CO₂ concentration. The current experiment does not support the proposition that global increases in carbon dioxide and temperature will increase the ratio of respiration to photosynthesis; rather, the data suggest that some plant species may continue to act as a sink for carbon even if carbon dioxide and temperature increase simultaneously.     

Growth Rate, Photosynthesis and Respiration in Relation to Leaf Area Index

This work examined three possible explanations of growth rateresponses to leaf area index (LAI) in which growth rate perunit of ground area (crop growth rate, CGR) increased to a plateaurather than decreasing above an optimum LAI at which all lightwas intercepted. Single leaf photosynthetic measurements, andwhole plant 24 h photosynthesis and respiration measurementswere made for isolated plants and plants in stands using Amaranlhushybridus, Chenopodium album, and two cultivars of Glycine maxgrown at 500 and 1000 µimol m^–2 S^–1 photosyntheticphoton flux density at 25 °C. CGR, relative growth rate(RGR), and LAI were determined from 24 h carbon dioxide exchangeand leaf area and biomass measurements. Respiration increasedrelative to photosynthesis with crowding in A. hybridus andthere was an optimum LAI for CGR. In contrast, the ratio ofrespiration to photosynthesis was constant across plant arrangementin the other species and they had a plateau response of CGRto LAI. Neither increased leaf photosynthetic capacity at highLAI nor a large change in biomass compared to the change inLAI could account for the plateau responses. It was calculatedthat maintenance respiration per unit of biomass decreased withdecreasing RGR in C. album and G. max, but not A. hybridus,and accounted for the plateau response of CGR to LAI. Sincesimilar decreases in maintenance respiration per biomass atlow RGR have been reported for several other species, a constantratio of respiration to photosynthesis may occur in more speciesthan constant maintenance respiration per unit of biomass. Amaranlhus hybridus L., Chenopodium album L., Glycine max L Merr, soybean, photosynthesis, respiration, growth, leaf area index     

Responses of trees to elevated carbon dioxide and climate change

The enhancement in photosynthesis at elevated concentration of carbon dioxide level than the ambient level existing in the atmosphere is widely known. However, many of the earlier studies were based on instantaneous responses of plants grown in pots. The availability of field chambers for growing trees, and long-term exposure studies of tree species to elevated carbon dioxide, has changed much of our views on carbon dioxide acting as a fertiliser. Several tree species showed acclimation or even down-regulation of photosynthetic responses while a few of them showed higher photosynthesis and better growth responses. Whether elevated levels of carbon dioxide can serve as a fertilizer in a changed climate scenario still remains an unresolved question. Forest-Air-Carbon dioxide-Enrichment (FACE) sites monitored at several locations have shown lately, that the acclimation or down regulation as reported in chamber studies is not as wide-spread as originally thought. FACE studies predict that there could be an increase of 23–28% productivity of trees at least till 2050. However, the increase in global temperature could also lead to increased respiration, and limitation of minerals in the soil could lead to reduced responses in growth. Elevated carbon dioxide induces partial closure of leaf stomata, which could lead to reduced transpiration and more economical use of water by the trees. Even if the carbon dioxide acts as a fertilizer, the responses are more pronounced only in young trees. And if there are variations in species responses to growth due to elevated carbon dioxide, only some species are going to dominate the natural vegetation. This will have serious implications on the biodiversity and the structure of the ecosystems. This paper reviews the research done on trees using elevated CO₂ and tries to draw conclusions based on different methods used for the study. It also discusses the possible functional variations in some tree species due to climate change.     

Responses of Respiration to Increases in Carbon Dioxide Concentration and Temperature in Three Soybean Cultivars

The purpose of this experiment was to determine how respirationof soybeans may respond to potential increases in atmosphericcarbon dioxide concentration and growth temperature. Three cultivarsof soybeans (Glycine max L. Merr.), from maturity groups 00,IV, and VIII, were grown at 370, 555 and 740cm³m^-3carbon dioxideconcentrations at 20/15, 25/20, and 31/26°C day/night temperatures.Rates of carbon dioxide efflux in the dark were measured forwhole plants several times during exponential growth. Thesemeasurements were made at the night temperature and the carbondioxide concentration at which the plants were grown. For thelowest and highest temperature treatments, the short term responseof respiration rate to measurement at the three growth carbondioxide concentrations was also determined. Elemental analysisof the tissue was used to estimate the growth conversion efficiency.This was combined with the observed relative growth rates toestimate growth respiration. Maintenance respiration was estimatedas the difference between growth respiration and total respiration.Respiration rates were generally sensitive to short term changesin the measurement carbon dioxide concentration for plants grownat the lowest, but not the highest carbon dioxide concentration.At all temperatures, growth at elevated carbon dioxide concentrationsdecreased total respiration measured at the growth concentration,with no significant differences among cultivars. Total respirationincreased very little with increasing growth temperature, despitean increase in relative growth rate. Growth respiration wasnot affected by carbon dioxide treatment at any temperature,but increased with temperature because of the increase in relativegrowth rate. Values calculated for maintenance respiration decreasedwith increasing carbon dioxide concentration and also decreasedwith increasing temperature. Calculated values of maintenancerespiration were sometimes zero or negative at the warmer temperatures.This suggests that respiration rates measured in the dark maynot have reflected average 24-h rates of energy use. The resultsindicate that increasing atmospheric carbon dioxide concentrationmay reduce respiration in soybeans, and respiration may be insensitiveto climate warming. Glycine max L. (Merr.); carbon dioxide; respiration; temperature; climate change     

Fitting photosynthetic carbon dioxide response curves for C(3) leaves

Photosynthetic responses to carbon dioxide concentration can provide data on a number of important parameters related to leaf physiology. Methods for fitting a model to such data are briefly described. The method will fit the following parameters: V(cmax), J, TPU, R(d) and g(m)[maximum carboxylation rate allowed by ribulose 1.5-bisphosphate carboxylase/oxygenase (Rubisco), rate of photosynthetic electron transport (based on NADPH requirement), triose phosphate use, day respiration and mesophyll conductance, respectively]. The method requires at least five data pairs of net CO(2) assimilation (A) and [CO(2)] in the intercellular airspaces of the leaf (C(i)) and requires users to indicate the presumed limiting factor. The output is (1) calculated CO(2) partial pressure at the sites of carboxylation, C(c), (2) values for the five parameters at the measurement temperature and (3) values adjusted to 25 degrees C to facilitate comparisons. Fitting this model is a way of exploring leaf level photosynthesis. However, interpreting leaf level photosynthesis in terms of underlying biochemistry and biophysics is subject to assumptions that hold to a greater or lesser degree, a major assumption being that all parts of the leaf are behaving in the same way at each instant.     

千烟洲马尾松人工林生态系统的碳循环模拟及模型参数的敏感性分析

应用改进后的碳水循环过程模型——景观尺度生态系统生产力过程模型(ecosystem productivity process model for landscape,EPPML)模拟了2003和2004年千烟洲马尾松人工林生态系统的碳循环过程,并对模型参数的敏感性进行了分析.结果表明:EPPML可用于模拟千烟洲马尾松人工林的碳循环过程,不仅总初级生产力(GPP)、生态系统净生产力(NEP)和生态系统总呼吸(Re)的年总值和季节变化与实测值十分吻合,而且也能反映极端天气对碳流的重要影响;千烟洲马尾松人工林生态系统具有较强的净碳吸收能力,但2003年生长最旺季的高温和重旱天气的耦合作用使其碳吸收能力明显低于2004年,2003和2004年平均NEP分别为481.8和516.6gC.m-2.a-1;马尾松生长初期的光照、生长旺期的干旱、生长末期的降水量是改变碳循环季节变化的关键气象条件;自养呼吸(Ra)与净初级生产力(NPP)的季节进程一致;异养呼吸(Rh)在年尺度上受土壤温度控制,而在月尺度上则受土壤含水量波动的影响;在生长季的丰水期,土壤含水量越大,Rh越小;而在生长季的枯水期,前两个月的降雨量越大,Rh也越大.EPPML参数中,25℃时的最大RuBP羧化速率(Vm25)、比叶面积(SLA)、最大叶N含量(LNm)、平均叶含N量(LN)、生物量与碳的转换率(C/B)对年NEP的影响最大;不同碳循环过程变量对敏感参数变化的响应也不尽相同,其中,Vm25和LN的增加能有效促进植物的碳吸收和呼吸;LN/LNm越小,对碳吸收和呼吸的抑制作用越强;C/B和SLA的增大会促进碳吸收,抑制呼吸.将全年区分为生长季与非生长季时得到的最敏感参数的结论与全年不尽相同.     

Woody tissue photosynthesis and its contribution to trunk growth and bud development in young plants

Stem photosynthesis can contribute significantly to woody plant carbon balance, particularly in times when leaves are absent or in ‘open’ crowns with sufficient light penetration. We explored the significance of woody tissue (stem) photosynthesis for the carbon income in three California native plant species via measurements of chlorophyll concentrations, radial stem growth, bud biomass and stable carbon isotope composition of sugars in different plant organs. Young plants of Prunus ilicifolia, Umbellularia californica and Arctostaphylos manzanita were measured and subjected to manipulations at two levels: trunk light exclusion (100 and 50%) and complete defoliation. We found that long‐term light exclusion resulted in a reduction in chlorophyll concentration and radial growth, demonstrating that trunk assimilates contributed to trunk carbon income. In addition, bud biomass was lower in covered plants compared to uncovered plants. Excluding 100% of the ambient light from trunks on defoliated plants led to an enrichment in ¹³C of trunk phloem sugars. We attributed this effect to a reduction in photosynthetic carbon isotope discrimination against ¹³C that in turn resulted in an enrichment in ¹³C of bud sugars. Taken together our results reveal that stem photosynthesis contributes to the total carbon income of all species including the buds in defoliated plants.     

Growth temperature can alter the temperature dependent stimulation of photosynthesis by elevated carbon dioxide in Albutilon theophrasti

Stimulation of photosynthesis in response to elevated carbon dioxide concentration [CO2] in the short-term (min) should be highly temperature dependent at high photon flux. However, it is unclear if long-term (days, weeks) adaptation to a given growth temperature alters the temperature-dependent stimulation of photosynthesis to [CO2]. In velveltleaf (Albutilon theophrasti), the response of photosynthesis, determined as CO2 assimilation, was measured over a range of internal CO2 concentrations at 7 short-term measurement (12, 16, 20, 24, 28, 32, 36 degrees C) temperatures for each of 4 long-term growth (16, 20, 28 and 32 degrees C) temperatures. In vivo estimates of VCmax, the maximum RuBP saturated rate of carboxylation, and Jmax, the light-saturated rate of potential electron transport, were determined from gas exchange measurements for each temperature combination. Overall, previous exposure to a given growth temperature adjusted the optimal temperatures of Jmax and VCmax with subsequently greater enhancement of photosynthesis at elevated [CO2] (i.e., a greater enhancement of photosynthesis at elevated [CO2] was observed at low measurement temperatures for A. theophrasti grown at low growth temperatures compared with higher growth temperatures, and vice versa for plants grown and measured at high temperatures). Previous biochemical based models used to predict the interaction between rising [CO2] and temperature on photosynthesis have generally assumed no growth temperature effect on carboxylation kinetics or no limitation by Jmax. In the current study, these models over predicted the temperature dependence of the photosynthetic response to elevated [CO2] at temperatures above 24 degrees C. If these models are modified to include long-term adjustments of Jmax and VCmax to growth temperature, then greater agreement between observed and predicted values was obtained.     

Responses of terrestrial ecosystems to temperature and precipitation change: a meta‐analysis of experimental manipulation

Global mean temperature is predicted to increase by 2–7 °C and precipitation to change across the globe by the end of this century. To quantify climate effects on ecosystem processes, a number of climate change experiments have been established around the world in various ecosystems. Despite these efforts, general responses of terrestrial ecosystems to changes in temperature and precipitation, and especially to their combined effects, remain unclear. We used meta‐analysis to synthesize ecosystem‐level responses to warming, altered precipitation, and their combination. We focused on plant growth and ecosystem carbon (C) balance, including biomass, net primary production (NPP), respiration, net ecosystem exchange (NEE), and ecosystem photosynthesis, synthesizing results from 85 studies. We found that experimental warming and increased precipitation generally stimulated plant growth and ecosystem C fluxes, whereas decreased precipitation had the opposite effects. For example, warming significantly stimulated total NPP, increased ecosystem photosynthesis, and ecosystem respiration. Experimentally reduced precipitation suppressed aboveground NPP (ANPP) and NEE, whereas supplemental precipitation enhanced ANPP and NEE. Plant productivity and ecosystem C fluxes generally showed higher sensitivities to increased precipitation than to decreased precipitation. Interactive effects of warming and altered precipitation tended to be smaller than expected from additive, single‐factor effects, though low statistical power limits the strength of these conclusions. New experiments with combined temperature and precipitation manipulations are needed to conclusively determine the importance of temperature–precipitation interactions on the C balance of terrestrial ecosystems under future climate conditions.